In the last 30 years, there has been an enormous progress in understanding the brain circuits involved in selective visual attention. Some current models propose that the 'attention signal' originates in high cortical areas (e.g. frontal and parietal cortex) and then is transferred in a top-down fashion to earlier stages in visual processing. This model is consistent with the existence of a rich anatomical network of feedback connections that go from higher to lower stages in the visual pathway. However, feedback connections reach stages as low in processing as the primary visual cortex (V-1 ) and the Lateral Geniculate Nucleus (LGN). Therefore, attention could potentially modulate perception by acting at the initial stages of the visual pathway. Consistent with this hypothesis, increasing evidence indicates that selective visual attention modulates the activity of V-1 and one recent anatomical study found the first evidence for attentional modulations in LGN. An important characteristic of selective visual attention is its retinotopic specificity the focus of attention can be restricted to very small regions of visual space. A remarkable specificity has been demonstrated in several cortical areas including V-1 but not in LGN. The demonstration that visual attention can modulate LGN activity is missing therefore an important piece of evidence. It is not known how retinotopically selective LGN modulations can be. In this proposal, the retinotopic specificity of LGN attentional modulations will be measured by simultaneously recording from multiple geniculate neurons while an animal performs a task that requires selective visual attention. In addition, it will be investigated whether LGN modulations are reliably transferred to V-1 by doing simultaneous recordings from LGN and V-1 cells with receptive fields aligned in visual space. A precise knowledge of the circuits involved in selective visual attention is important to understand how the brain processes visual information. The study of this circuitry will eventually lead to the prevention and treatment of serious attentional deficits that are common in many psychiatric and neurological disorders.